1. Field of the Invention
The present invention relates to a method and apparatus for establishing a radio link between a mobile terminal and a network in a wireless communication system.
2. Description of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A related art UMTS network structure 1 is illustrated in FIG. 1. A mobile terminal 2, or user equipment (UE), is connected to a core network 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains, and manages a radio access bearer for communications between the UE 2 and the core network 4 to meet end-to-end quality of service requirements.
The UTRAN 6 includes a plurality of radio network subsystems (RNS) 8, each of which comprises one radio network controller (RNC) 10 for a plurality of base stations 12, or “Node Bs.” The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. One or more cells exist in one node B. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit downlink signals to the UE. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer to the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and the UTRAN 6 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is a well-known in communications systems.
A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into the physical layer, the data link layer, and the network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (transmitter).
The MAC layer of the second layer (L2) provides information transfer service to a higher layer and is linked via a logical channel to a radio link control (RLC) layer. The RLC layer of the second layer (L2) supports the transmission of reliable data and can perform segmentation and concatenation functions for RLC service data units (SDU) received from an upper layer.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls transport channels and physical channels with respect to the establishment, re-establishment, and releasing of radio bearers. A radio bearer (RB) is a service provided by a lower layer, such as the RLC layer or the MAC layer, for transferring data between the UE 2 and the UTRAN 6.
The establishment of an RB determines regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE 2 and an RRC layer of the UTRAN 6, the UE 2 is said to be in the RRC-connected state. Without such connection, the UE 2 is in an idle state.
Hereafter, a Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) will be described. MBMS refers to a method of providing streaming or background services to a plurality of UEs 2 using a downlink-dedicated MBMS radio bearer that utilizes at least one of point-to-multipoint and point-to-point radio bearer. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals through the MBMS radio bearer only while the session is ongoing.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs 2 within a broadcast area, for example the domain where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE 2 group within a multicast area, for example the domain where the multicast service is available.
The UTRAN 6 provides the MBMS service to the UEs 2 using the RB. RBs used by the UTRAN 6 can be classified as a point-to-point RB or a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel) or SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a unidirectional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel), and the physical channel SCCPCH. The logical channel MTCH is configured for each MBMS service provided to one cell and used to transmit user plane data of a specific MBMS service to the UEs 2.
The UTRAN 6 providing the MBMS service transmits MBMS-related RRC messages to the plurality of terminals (UEs 2) through an MCCH (MBMS Control Channel). Herein, the logical channel MCCH is the point-to-multipoint downlink channel and is mapped to the FACH, which is mapped to the SCCPCH.
The MBMS-related RRC messages transmitted through the MCCH typically comprise an MBMS service information message and an MBMS RB information message. The MBMS service information message transmitted to each cell includes a list of IDs for MBMS services ongoing, or set to be ongoing, in a corresponding and the type of RB for each MBMS service. If the specific MBMS service uses the point-to-multipoint RB in the corresponding cell, the MBMS RB information message includes information of the point-to-multipoint RB related to the corresponding MBMS service.
A terminal desiring to receive the specific MBMS service using the point-to-multipoint RB receives the MBMS service information message through the MCCH. If the received MBMS service information message indicates receiving the MBMS RB information message for the specific MBMS service, the terminal obtains information required for establishing an MBMS RB for receiving the specific MBMS in the terminal through the MBMS RB information message. In other words, if the received MBMS service information message includes an ID of the specific MBMS service and indicates that a type of RB for the specific MBMS is a point-to-multipoint RB, the terminal obtains point-to-multipoint RB information by receiving the MBMS RB information message and establishes the point-to-multipoint RB by using the information.
A related art process for establishing the MBMS RB for the specific MBMS service in a cell into which the mobile terminal (UE 2) has moved is illustrated in FIG. 3. As shown in FIG. 3, the mobile terminal moves from a cell A to a cell B, from the cell B to a cell C, and then from the cell C to the cell A. The UE 2 sequentially performs the steps 1, 2, 3 and 4 in the cells A-C.
The cells A-C provide a specific MBMS service the mobile terminal (UE 2) desires to receive, and transmit the MBMS service to the mobile terminal using a point-to-multipoint RB. Whenever the mobile terminal moves into a new cell, it receives an MBMS service information message and an MBMS RB information message. The UE 2 then establishes the point-to-multipoint RB for the new cell using the received information messages.
In step 1, the mobile terminal is positioned in the cell A and a session of the specific MBMS service desired to be received by the mobile terminal starts at this time. When the session starts, the mobile terminal receives an MBMS RB information message transmitted in the cell A and obtains information for a point-to-multipoint RB. The mobile terminal then establishes a point-to-multipoint MBMS RB using the obtained point-to-multipoint RB information and receives data of the specific MBMS service. Subsequently, the mobile terminal moves from the cell A to the cell B for performing step 2.
Thereafter, in steps 2, 3 and 4, the mobile terminal receives an MBMS RB information message transmitted from the corresponding cell while moving from one cell to other, and obtains point-to-multipoint MBMS RB information. The mobile terminal then establishes the point-to-multipoint MBMS RB using the obtained point-to-multipoint RB information and receives data of the specific MBMS from the corresponding cell.
According to the related art radio bearer establishing method of a mobile terminal, whenever the mobile terminal receives a specific MBMS service through a point-to-multipoint RB while moving through several cells, the mobile terminal will have received an MBMS RB information message for establishing an MBMS RB each time the mobile terminal moves into a cell. Accordingly, like step 4 of FIG. 3, when the mobile terminal returns to a cell previously entered into, such as the cell A, after passing through the other cells (cells B and C), the mobile terminal unnecessarily receives again the MBMS RB information message it had previously received for establishing the MBMS RB. This operation is problematic because the unnecessary reception of the MBMS RB information message causes a time delay in receiving MBMS service data after the mobile terminal moves into the cell and the MBMS RB is set. Furthermore, data is lost because the data cannot be received due to the delay.